Method of diamond growth and apparatus therefor



April 24, 1962 H. P. BOVENKERK 3,031,269

METHOD OF DIAMOND GROWTH AND APPARATUS THEREFOR Filed Nov. 27, 1959 2Sheets-Sheet l 1 IIIIIII IIIIIIIIIIIIIII 399 x In venfor y Hora/0 P.fiovenlrer/r His A flame y 2 Sheets-Sheet 2 H. P. BOVENKERK METHOD OFDIAMOND GROWTH AND APPARATUS THEREFOR Filed Nov. 2'7, 1959 April 24,1962 United States Patent 3,tl31,269 METHGD 0F DIAMOND GRGWTH ANDAPPARATUS TEIEREFQR Harold P. Bovenkerk, Royal Gait, Mich, assignor toGeneral Electric Company, a corporation of New York Filed Nov. 27, 1959,Ser. No. 855,787 15 Claims. Cl. 23-2091) This invention relates to animproved method and apparatus for growing good quality and largerdiamond crystals, and more particularly to the feature of temperaturecontrol and its effect on diamond growth.

While'it has been stated that this invention relates to the growth ofdiamond crystals, the word growth is employed in its broader sense toinclude or to represent the transformation or change of a carbonaceousmaterial, which is a non-diamond form of carbon, to diamond. Oneapparatus capable of obtaining and sustaining the high pressures andhigh temperatures necessary for diamond growth has been adequatelydisclosed and claimed in a copending application S.N. 707,432, H. TracyHall, filed January 6, 1958, now US. Patent 2,941,248, and assigned tothe same assignee as the present invention, and a method of converting anon-diamond form of carbon to diamond has also been adequately describedand claimed in copending application S.N. 707, 435, H. Tracy Hall etal., filed January 6, 1958, now U. S. Patent 2,947,610, and assigned tothe same assignee as the pres ent invention. By reference, thedisclosures of the aforementioned applications are incorporatedherewith. In the elapsed time since the invention of the subject matterof the above-identified applications, considerable effort has beenexpended towards improving not only the particular method and apparatusas described in the aforementioned copending applications, but moreparticularly toward improving the quality of the diamond crystal itself. For example, investigations have been made towards producing aclearer or better quality crystal, a better formed crystal, a greateryield of crystal, and also a larger crystal. In some instances,improvements obtained have been combinations of those featuresmentioned; however, improvements in crystal size have been limited, andwhether larger or smaller crystals are grown has been generally left tothe reaction carried on within wide ranges of conditions without anyexplicit defining parameters for particular crystal growth. It is, ofcourse, highly desirable that larger crystals be obtained for a varietyof purposes not only for those industrial applications where single andlarger crystals are widely employed as cutting and grinding elements,but also 'for gem use and other well known diamond applications too.numerous to mention at this time.

Accordingly, it is an object of this invention to provide a largerdiamond crystal.

It is another object of this invention to provide an improved method forobtaining larger diamond crystals.

it is another object of this invention to define growth parameters forlarge diamond crystals.

It is yet another object of this invention to provide a temperaturecontrol method for growing larger diamond crystals.

It is again another object of this invention to increase reaction volumefor good diamond crystal growth.

It is another object of this invention to provide a specific range ofpressures and temperatures and a method of reaching these pressures andtemperatures where good diamond crystals of large size are grown.

It is yet another object of this invention to provide specific reactionvessel configurations which together with specified heating meansprovides, when using the methods of this invention, larger diamondcrystals.

Briefly described, this invention in one form comprises ice placingreaction material which is a catalyst and a nondiamond form of carbon ina reaction vessel in such a manner that the reaction material isindirectly heated and thereafter raising the pressure and temperature ina specified manner to a predetermined range where large diamond crystalsmay be grown.

This invention will be better understood when taken in connection withthe following description and the drawings in which;

FIG. 1 is an illustration of the high temperature high pressureapparatus described as the belt;

FIG. 2 is an enlargement and assembled view of the center portion ofFIG. 1 illustrating a reaction vessel and gasket assembly;

FIG. 3 illustrates a series of curves each defining a.

diamond growing region for a particular catalyst;

FIG. 4 is one form of a reaction vessel employing indirect heating;

ferred diamond growing area within a given region.

Various types of apparatus are available which. will.

maintain required high pressures and high temperatures necessary fordiamond growth conditions. FIG. 1 is exemplary of one preferred form ofapparatus together with appropriate proportion and scale.

Referring now to FIG. 1, there is illustrated what has been previouslyreferred to as a belt apparatus 10. Apparatus 10 includes a pair ofpunch assemblies 11 and 11 together with a lateral pressure resisting orbelt member assembly 12. Since the punch assemblies 11 and 11 aresimilar in nature a description of one sufiices for the other. Punchassembly 11 includes a central punch 13 of a hard material, such as toolsteel, cemented tungsten. carbide etc. which is surrounded by aplurality of binding rings 14, 15 and 16. Punch 13 has a generallynarrowing tapered portion 17, the taper of which is a smooth diametricalincrease from the pressure area or surface 13 axially along the lengthof the punch to a given larger area 19. Tapered portion 17 includes anend portion 20 offrusto-conical configuration with, for example, an-

of punch 13 while subjecting each cross section to thesame total forceas is imposed upon area 18.

Another principle employed to enable punch 13 to resist fracture isprestressing. In FIG. 1, punch 13 is prestressed by being mountedconcentrically within a plurality of metal annular, backing or bindingrings 14, 15 and 16. These binding rings may be assembled by well knownmethods of press fitting or shrink fitting. For example, punch assembly11 consists of a punch 13, two hardened alloy steel press fittingbacking rings 14 and 15, and an outer soft steel guard ring 16.Interference and proper stressing is supplied in one form by providing ataper and interference on each of the mating surfaces. When theabove-mentioned binding rings are employed together with a Carboloycemented carbide punch 13, fracture is maintained at a minimum. Theprincipal'function of the binding rings is to provide sufiicientradially inward compressive force on punch 13 to oppose the radiallyoutward force developed within the punch and to prevent the punch fromfracturing at high pressures.

In considering the role of the binding rings 14, 15 andmaterial and fitof the rings and punch may be variedconsiderably from the dimensionsgiven, due considera- 3 tion always being given to the forces andpressures to be withstood.

Punch assemblies 11 and 11' are employed in conjunction with a lateralpressure resisting or die assembly 12, comprising a die 21 having acentral opening or aperture 22 therein which is defined by a tapered orcurved wall surface 23. Wall surface 23 generally describes a narrowingtapered or convergent die chamber or opening into which punches 13 and13' may move or progress to compress a specimen or material, forexample, a reaction vessel as illustrated in FIG. 2. This combination oftapered punches and tapered die chamber contributes to the strength ofboth punches 13 and 13 and die 21.

In order to minimize failures, die 21 is also made of a high strengthmaterial, such as Carboloy cemented carbide, for example, grade 44A,similar to that of punch 13. Prestressing of die 21 may be achieved inthe same manner as prestressing of punch 13. Tapered wall 23 of chamber22 is prestressed to its limitative hoop compression. Binding rings 24and 25 are employed for purposes similar to rings 14 and 15 as describedand are preferably of the materials, while ring 26 is preferably of lowcarbon steel similar to ring 16. Binding rings 24 and 25 and die 21increase in height to provide approximately a 7 taper with thehorizontal, a taper which provides an increase in cross section ofmaterial for imposed forces in the same manner as the taper of thefrusto-conical portion of punch 13. In the embodiment illustrated inFIG. 1, tapered wall 23 includes a pair of frusto-conical sections 27and 27 meeting at a horizontal center line of die 21 and having an angleof about 11 to the vertical. In order to provide motion or stroke forpunches 13 and 13' to permit these punches or one of them to move intothe chamber 22 to compress a reaction vessel or specimen therein, agasket is employed between the opposed tapered surfaces of the die 23and punch 13.

A gasket must have the property of gripping the surfaces of the punchand die and be capable of undergoing large plastic shear distortionswithout losing shear strength. The shear strength of the material shouldbe great enough to prevent gasket blow-out during all parts of theoperation cycle, yet not resist movement of the punch excessively. Theforce imposed upon the gasket structure is not uniform, but varies froma maximum adjacent the innermost edge of the frusto-conical portion'ofthe punch to a minimum at the outer extremity adjacent the 7 taperedportion 28.

A gasket serves several functions including; first, sealing in thecontents of the chamber; second, allowing a rather large movement of thepunch relative to the die; and third, providing electrical insulationbetween the die and the punches when resistance heating is employed.

Among materials having these general properties are certain ceramics orstones, for example, wonderstone (a homogeneous pyrophyllite stone).Minnesota pipestone (catlinite) also has satisfactory physical andchemical properties for this purpose.

There is also provided a metal gasket, for example mild steel, as thecenter element of a composite gasket sandwich structure to impartcohesiveness, tensile strength and ductility to the gasket structure asa whole. In addition, a metal which has the correct properties ofdrawing out uniformly without tearing, while work hardening in so doing,adds considerably to the confining strength of the gasket structure.

FIG. 1 provides an exploded view of the sandwich type frusto-conicalgasket assembly 30 which surrounds tapered surface 17 of punch 13, andcomprises a pair of thermally and electrically insulating, pressureresistant frusto-conical ceramic or stone gaskets 31 and 32 with ametallic frusto-conical gasket 33 between adjacent gaskets 31 and 32.Not only does gasket 31 serve to electrically in- Sulate the punch fromthe die, but also gaskets 32 on punches 13 and 13 meet in abuttingrelationship in chamber 22 to provide a liner or insulator therefor.Although specific configurations and compositions of gasket assembly 30have been described above, it is obvious that any suitable gasketassembly meeting the requirements described may be employed.

One form of reaction vessel 34 is illustrated in FIG. 2. Referring nowto FIG. 2, reaction vessel 34 is approximately 0.350 inch in diameterand 0.450 inch in length positioned in chamber 22 between punches 13 and13 and includes a cylinder 35 of electrically insulating material suchas prophyllite or catlinite, talc, etc, positioned between a pair ofspaced electrically conductive discs 36 and 36'. A washer assembly 37 ispositioned between each punch 13 and 13' and its associated disc 36 andcomprises a heat insulating core '38 with a surrounding outer electricalconductive ning 39 in contact with punches 13 and 13, to complete thereaction vessel. Rings 39 and 39 are preferably of a hard steel andtogether with cores 38 provide a cap assembly for reaction vessel 34which thermally insulates the centers of the punch faces and provides acurrent path to the material in reaction vessel 34. The punch and dieassembly of FIGS. 1 and 2 is positioned between platens or pistons ofany suitable press apparatus to provide motion of one or both punches.

Each punch assembly is provided with an electrical connection (FIG. 1)in the form of an annular conducting ring 40 or 40' with connectors 41and 41, to supply electric current from a source of electrical power(not shown) through punch assemblies 11 and 11, to a high temperaturehigh pressure reaction vessel 34.- Pressure is applied to the vessel 34by movement of one or both punches 13 and 13' towards each other in apress apparatus. At the same time, electric current is supplied from oneelectrical connector, such as upper connector 41 to upper conductingring 40 to the punch assembly 11. Referring then to FIG. 2, currentflows from punch 13 to ring 39 and disc 36. From this point, currenteither flows through a suitable heater provided in the reaction specimenor through the specimen itself. The current path continues from lowerdisc 36', ring 39' to punch 13'. Referring again to FIG. 1, the currentpath continues through punch assembly 11, conductor ring 40' andconnector 41' to the electrical source (not shown).

Pressures have been measured in this apparatus by a Well known method ofutilizing the fact that certain metals undergo distinct changes inelectrical resistance at particular pressures. For example, bismuthundergoes a phase change which results in a change of electricalresistance at 24,800 atmospheres, thallium undergoes such a phase changeat 43,500 atmospheres, cesium at 53,500 atmospheres, and barium at77,400 atmospheres. Thus, by determining the hydraulic press loadnecessary to cause a phase change in the metals mentioned, individualpoints on a pressure-press load curves are determined. By insertinggermanium in reaction vessel 34, applying various press loadscorresponding to those obtained by phase changes and heating thegermanium to the temperature at which the germanium melts, as measuredby a large decrease in electrical resistivity, a series of points on apressure-melting point curve for germanium is determined.

Temperature in the reaction vessel is determined by fairly conventionalmeans such as by placing a thermocouple junction in the reaction vesseland measuring the temperature of the junction in the usual manner.Electrical energy at a predetermined rate is then supplied the apparatusand the temperature produced by this power is measured by thethermocouple assembly. This same procedure is repeated a number of timeswith different power inputs to produce a calibration curve of power.

The following is one specific example of a transformation ofcarbonaceous material to diamond as carried on in apparatus similar tothat of FIG. 1.

Example I The reaction vessel of FIG. 2 was assembled employingalternate small solid cylinders of commercially obtained graphite ofspectroscopic purity and nickel, 99.6% nickel. The vessel was subjectedto a pressure of about 90,000 atmospheres together with a temperature ofabout 1600 C. These conditions were maintained for about 3 minutes.After removal from the apparatus the reaction vessel was found tocontain diamonds.

Literally, s of thousands of carats of diamonds (incontrolvertiblydiamond) have been produced by this apparatus and similar examples.Diamonds so produced are presently commercially available.

The present invention to be applied to the foregoing description of oneexemplary method and apparatus, is temperature control. This controlshould be as precise as possible under existing conditions. Pressure andtemperature in the reaction vessel are constantly changing because ofchanging internal conditions. During and upon reaching the desiredtemperatures, some parts of the apparatus expand while others melt witha corresponding reduction or increase in volume. For example, stoneloses volume due to a phase change and metal increases in volume when itmelts, pressure causes contraction of the reaction vessel and contentsbecause of such occurrences as filling of voids and generalcompressibility of the pants employed. It is, therefore, desirable thatthe changes relating to increase in Volume and the changes relating todecrease in volume balance each other and it is believed that this issomewhat true as indicated by pressure and temperature measurements overliterally hundreds of operations. It has been discovered, however, thatreasonably precise temperature and pressure control is necessary for theformation, not only of a better quality diamond but, even morenecessary, in order that larger crystals of good quality may be grown. Achange of conditions in a reaction vessel, even though small incomparison to a range of pressures and temperatures wherein desirableresults are attained, affects the diamond reaction much more vigorouslythan had been previously realized. Accordingly, it has been discoveredthat control of temperature is as important as the control of pressureand that the whole reaction may be regulated by temperature control. Itmust be remembered, however, that the control of temperature doesprovide in effect, and indirectly, some control over pressure. It alsomust be understood that there are no means at present for accuratelymeasuring the pressure in the reaction vessel with great precision whilebeing heated in the 50 to 100,000 atmosphere pressure range and above.That there is a need of temperature control and also pressure control ismore clearly understood when taken in connection with the followingdescription of diamond growth conditions.

It has been discovered as described in the previously filed applicationsabove-mentioned, that a catalyst should be employed in the reaction forgood diamond growth conditions. These catalysts include generally thosemetals of the group VIII metals of the periodic table of elements andalso manganese, tantalum and chromium. Catalysts may be employed invarious forms, such as for example, elemental metal form, alloys of suchmetals, and numerous other arrangements and configurations. Alloyspermit lower pressure operation and their description and operatingparameters are best described in copending application S.-N. 655,885, H.M. Strong, filed April 29, 1957, now abandoned and continuation-in partthereof of SN. 707,433, now U.S. Patent 2,947,609, and assigned to thesame assignee as the present invention. The subject matter of thatapplication is incorporated herewith. However, not all catalysts willprovide diamond growth in the same range of pressures and temperatures,since it has been further discovered that there exists a defined rangefor each catalyst metal and/ or also for each alloy and for each alloycomposition.

In FIG. 3, there is illustrated a group of exemplary curves definingindividual ranges of pressures and temperatures for diamond growth forgiven catalyst. In FIG. 3, curves F, N, R, P and T represent iron,nickel, rhodium, palladium and platinum respectively. Other catalystsand combinations provide similar curves. These indicated ranges have notbeen determined with absolute precision or defined with high exactness,but have been determined by numerous tests and experiments of hundredsof individual runs to define a region where diamonds are either formedor not formed with a particular catalyst. It should be noted that theright-hand portions of the curves generally define a theoretical line ofseparation of the diamond and non-diamond phases of carbon, or agraphite-to-diamond equilibrium line. Such a line is generally referredto as the diamond-to-graphite equilibrium line on the phase diagram ofcarbon. The position of this line has been determined by the pressureand temperature measuring methods set forth in this application inconjunction with hundreds of operations determining pressures andtemperatures Where diamonds grow or do not grow. Temperaturemeasurements, for example, were obtained with commercially availableplatinum-platinum rhodium (the rhodium being 10%, by Weight, of thetotal Weight of the platinum and rhodium), chromel-alumel,rhodium-platinum, etc. thermocouples. The thermocouple junctures werepositioned generally centrally within the reaction chamber with leadwires extending laterally opposite through carefully drilled holes inthe reaction vessel and then through holes in the gasket assembly to themeasuring apparatus. High pressure effects on these and otherthermocouples were not found to be seriously affecting the readingobtained.

Insofar as knowledge of diamond growth reaction has progressed, theparticular catalyst metal must undergo some degree of melting or solidsolution before transformation to diamond takes place. Therefore, thebottom or lowermost portion of the curves are defined generally by themelting temperature of the particular catalyst in the presence of carbonat the given pressure. The lefthand portion of the curves are generallystraight and nearly vertical lines since the points therealong aredetermined by the melting temperature of the catalyst in the presence ofcarbon at the given pressures, an approximately linear function. In thecourse of concentrated experimentation not only to ascertain theseexemplary curves but also simply to make diamonds, there wereindications that the diamonds formed were not always of the same grade,size, quantity or quality for every curve point established, althoughcertain areas within a given curve provided repetitious growths ofsimilar quality. Diamond growth at the points establishing a curve iseffected by the heretofore described changing temperature and pressureconditions, so for example, referring to any point within any curve ofFIG. 3 generally adjacent the lower end on the curves, it is understoodthat a slight change in pressure and temperature may cause change ofconditions out of the diamond growth region into the graphite regionresulting in either no diamonds grown or, depending on the degree ofchange, graphitization of previously grown diamond. Such change may ormay not take place, and the frequency or degree or rapidity there of, orthe exact point at the completion of the test where pressure andtemperature have remained constant may not be accurately ascertained.Because of these and other reasons and also that it is difficult todetermine the precise reaction taking place, variations in diamondsamples are found at points Within a given curve close to the linedefining the curve. Temperature changes which permit movement in and outof the diamond range are more clearly understood when examined in lightof the configuration of one prior reaction vessel, for example, thatindicated in FIG. 2.

In FIG. 2, reaction vessel 34- is heated, in one form, by resistanceheating. Accordingly, when pressure and temperature are raised toproceed into the diamond growing region defined by a particular catalystcurve, carbon transforms from the non-diamond form to diamond. However,in so doing, the resistivity of the sample changes drastically as moreand more carbon transforms from the electrically conducting carbon formto electrically nonconducting diamond. It is, therefore, apparent thatthe final temperature or resistance heating may depend on such variablesas the volume of carbon, the shape, the amount of diamond formed,formation rate, position of the crystals formed in the reaction vessel,changes of resistance with respect to temperature and other variables.In one respect, a further problem is encountered when employing largerreaction vessels. Larger vessels are employed for purposes including, toincrease the yield of diamonds per run, and to increase the availablevolume for larger crystal growth. In the larger vessels, however, thetime delay of temperature rise is of such length that it is extremelydifficult to control by merely varying the power input, or by attemptingto foresee conditions before their actual occurrence. A proposed andgenerally certain method of growing diamonds therefor has been anattempt to establish some sort of control at about the central portionof a given catalyst curve indicating a diamond growing region of aparticular catalyst.

This invention, therefore, in one part, discloses an improved reactionvessel in which temperature can be more precisely controlled. Oneprinciple upon which this invention is based is temperature control.Temperature control is achieved, then, in the first instance throughchoice of materials and/or the arrangement of these materials in apreferred configuration. Although the reaction vessel illustrated inFIG. 2 has been described as being particularly susceptible to widevariations in temperature, proper choice of parts may minimize thesevariations. For example, the use of thicker or thinner end discs 36 aswell as discs of greater or less electrical and thermal conductivitywill provide different degrees of heating and will affect changes of theposition of the hotter zone in the reaction vessel. The use of copperdiscs with high electrical and heat conductivity increases the heatingat the central portion of the vessel, while lesser conductive metalsincrease the heating at the end portions of the vessel. Therefore, bychoice of proper end discs and catalyst metals, a generally uniformdegree of heating in the vessel may be established. Where the reactionvessel is quite small as described for FIG. 2, the time interval fromthe application of power to the proper temperature rise is quite small,for example, 1 to seconds. Therefore, changes in temperature may bequickly adjusted for in order to maintain constant temperature. Thedisadvantages of such a reaction vessel in practicing this invention inbest form include, first, that with increasing size of vessel the timeinterval is proportionately longer, and control more difiicult, andlarger vessels are physically necessary for larger crystal growth,second, that the vessel configuration under prolonged conditions of hightemperature and high pressure develops leaks or the stone materialsdecompose with the products thereof affecting the reaction. So, forlarger crystal formation in larger vessels, at substantially constanttemperatures for prolonged periods, it has been discovered that indirectheating in the first instance, coupled with an advantageous vesselconfiguration provides excellent results and overcomes the priordiscussed problems. Indirect heating in one form has been disclosed incopending application S.N. 488,027, Strong, now US. Patent 2,941,241,assigned to the same assignee as the present invention. In the Strongapplication, indirect heating is illustrated as a platinum wiresurrounding a lava tube. While this type of indirect heating providesmore of a temperature control than direct heating, it does not rise tothe level of control necessary to practice this invention, because, ingeneral, the platinum wire cannot carry the required current necessaryto reach the higher temperatures, because the resistance of platinumwire changes greatly at the higher temperatures, because of reactionbetween the platinum and the stone, and more importantly, because thecarbon undergoing transformation is next adjacent stone or pyrophyllite.It has been found, for the benefits to be obtained by this invention,that materials such as wonderstone, pyrophyllite or catlinite not beused adjacent the catalyst, or the carbon which undergoestransformation, simply because that for the longer runs, i.e., for aboutminutes and longer, and at the higher temperatures, it has beendiscovered that melting or decomposition of these stones occurs, and themelt or the products of decomposition adversely affects the diamondreaction so that fewer and poorer diamonds are recovered.

In order to grow diamond crystals of relatively large size and goodcrystal quality in any system, the conditions of the growth must beprecisely controlled with respect to temperature and pressure. Also,such a system must permit temperature to be maintained constant withtime. A reaction vessel which is particularly adaptable to this controlis indicated in FIG. 4.

In FIG. 4, there is illustrated a reaction vessel which comprises in oneexample a pyrophyllite cylinder 51 of about inch wall thickness and %1inch outside diameter. Placed concentrically Within the cylinder 51 isheating tube 52 of graphite, for indirect heating, which lies adjacentto and contiguous with cylinder 51. A further cylinder 53 of alumina isplaced within the graphite heater tube 52 to the adjacent thereto.Graphite 54 from which diamonds are grown in is then placed in a diamondmetal catalyst tube 55 and thereafter positioned centrally within thealumina cylinder 53. For other applications, 54 may be other reactantsand tube 55 other catalysts. A plug of alumina 56 and 56 (not shown)fits with the upper and lower portions of graphite heater tube 52 tosupport and insulate the graphite and catalyst in the same manner asdoes the sides of vessel 56. Only one plug may be necessary forresistance heating since a single plug will prevent an electric circuitthrough the graphite. Suitable end discs 57 and 57 are provided toconvey current to heater tube 52. Alumina cylinder 53 should be of thepre-fired variety so that it is relatively soft. Pre-firing is a firingtemperature of about 1100 to l200 and generally not over thistemperature because the alumina then becomes hard fired. Hard firedalumina is a deterrent to substantial hydrostatic pressure transmissionat the higher pressures and temperatures. Other ceramic materials, suchas zirconia, magnesia and boron nitride for example may also be employedfor cylinder 53. Alumina cylinder 53, in one example, was of acommercial grade, 96 to 99+% aluminum oxide, with the remaindermaterials of a nature not affecting the diamond growing reaction, andabout .0l0.050 inch in thickness. A general range of about .030-.100inch thickness provides good results.

Graphite heater tube 52 is preferably spectroscopically pure, 99+graphite with no impurities which will decompose or change electricalresistance at high pressures and temperatures.

This type of reaction vessel provides the important features of a vesselin that it will not leak under high pressure and high temperatureconditions, maintains a practically constant (temperature over all ofthe graphite undergoing transformation both in the vertical andhorizontal directions, maintains its particular geometry under the highpressures and high temperatures, and provides a heater tube, i.e.,graphite, whose resistance does not change appreciably under highpressures and temperatures and, therefore, constant heating is obtained.The desired geometric stability and the prevention of extensive catalystintermixing are achieved by insulating the reactants from the heatertube with such materials as alumina, zirconia, magnesia, etc'. Themolten catalyst wets alumina cylinder 53 and causes it to remain intact,sealed, protected, etc., since the alumina becomes entirely covered withthe catalyst. This also permits heating the reactants to any reasonabletemperature up to at least the melting point of the insulation with nochange in geometry with respect to time. The use of a metal catalyst intube form permits sbstantial compression of the reaction vessel togetherwith marked decrease in axial dimension without cracking or leaking ofeither the cylinder 53 or the tube, which would result in thedecomposition products or melt of the cylinder 51 affecting the diamondreaction. Tube 55 being also of good thermal conductivity aids inavoiding a large axial temperature gradient. A further advantage of thissystem is that when diamond starts to grow inwardly from the catalysttube, the growth is in the direction of extremely low temperaturegradient. This also provides better control of the diamond growingconditions and reduces the rate of growth. The result of using thesestable growing conditions is the production of a larger diamond crystal.For example, using nickel as a catalyst, it has been possible to growdiamond crystals from 500 microns to over 1 millimeter in length(considerably larger than by any other system) with pressures in theregion of 76 to 78 kiloatmospheres, a temperature of 1500 centigrade,and a growth rate period of about 30 minutes.

Together, with larger vessels, at modification of an indirect heatingreaction vessel may be employed. In FIG. 5, there is illustrated amultiple concentric cylinder vessel 60. Vessel 60, in one example,includes an outer cylinder 61 similar to cylinder 51 of FIG. 4. Agraphite heater tube 62 is positioned concentrically within cylinder 61to provide resistance heating. Thereafter, a cylinder of alumina 63 ispositioned within graphite tube 62 to act as insulation and a catalyststabilizer. The core of the reaction vessel includes a central rod 64 ofalumina about which is a tube of catalyst metal 65. Catalyst metal tube65 is surrounded by a cylinder of graphite 66 for diamond growth, andanother cylinder 67 of catalyst metal. It is thus understood thatdiamond growth occurs in an annular space represented by graphitecylinder 66. While the space available is limited, barring an increasein size of the vessel, there is provided an increase in stabilizedcatalyst surface area for better diamond growth in addition to increasedtemeprature control with diamonds growing in an area of low temperaturegradient and removed from the center of the vessel.

Insofar as this description has proceeded, there has been disclosed anoperative example of a high pressure high temperature apparatus in whichthe invention is to be practiced, together with preferred and modifiedforms of reaction vessels in which the diamonds are to be grown withrespect to a temperature control principle. In conjunction with theapparatus and the reaction vessel, there has been described the diamondforming regions of pressure and temperature necessary to grow diamondcrystals. The remaining principle to be described in this invention is amethod and a preferred range to be employed, utilizing the pressapparatus and reaction vessels as heretofore described and disclosed.

Referring now to FIG. 6, there is illustrated, for the purposes ofexplanation, the diamond forming region as previously determined for analloy of 80% nickel and 20% chrome (by weight) as a catalyst. It is arelatively simple manipulation to increase the pressure and temperatureof the reaction vessel in accordance with this invention to the rangeenclosed by the curve OA and OB. Now that the reaction vessel is of sucha nature that the temperature may be more precisely controlled FIGS. 4and 5 particularly), the following results have been found. When raisingthe pressure and temperature to the general area indicated by O, A, C,D, and maintaining that temperature within controlled limits from a fewseconds to an hour or longer, it has been found that the diamondcrystals grow in the form of cubes, which are generally of a very poorgrade, and black in color. For the purposes of description, this regionis hereinafter referred to as the cube region. The upper limit ofextension of line DEC is unknown as is the upper extension of line OA.When increasing temperature to reside in the further area generallyincluded within curve FEC, as a result of many tests, some ranging froma few seconds to an hour or longer, it has been found that diamondcrystals grow extremely fast and in very high yield, but that individualcrystals themselves are generally of a poor quality and small. It hasbeen found that when pressures and temperatures are adjusted to liewithin curve PEG and in the right-hand portion thereof, diamond crystalsgrow very quickly and, while generally small, are of a good quality andgrade. In the many operations previously referred to, to define curve OBbetween the diamond forming and graphite regions no large crystals weregrown because of many reasons including, the short pe riod of time usedfor growing diamonds, lack of temperature control for extended periodstogether with lack of a proper constant temperature reaction vessel andalso of knowledge of the effect of temperature control in specificareas. It has been discovered that a range exists along the line DBwherein by precise control of time and temperature extremely largeexcellent quality crystals may be grown. The total region for thecatalysts mentioned may be defined as commencing at about 1200 C. and60,000 atmospheres ranging upwardly to points unknown and lying justinside the diamond growing region along the line DB as indicated by theshaded area in FIG. 6. It is more desirable to maintain temperature andpressure conditions at the lower extremity of this range just above thecube region and adjacent the line DB or the area within the curve DEFand DE. The width of the shaded area is about 50 C. Therefore, the areabeing just above the cube region and just inside of the righthandportion of the curve DB is well defined. Here diamend growth rate isconsiderably slowed. In actual practice, to maintain a temperaturewithin this abovedescribed area is extremely difficult, because in priorap para-tus, temperature varies as described, and the defined area is solimited that a small temperature change may result in conditions beingcompletely out of the area to the left of the curve DB and out of thearea to the right of the curve DB with no absolute certainty where thetemperature is. However, the described shaded area is the desired oneand the only area thus far found wherein the largest good crystals sofar produced have been grown.

No other large reaction vessel has been satisfactory so far inattempting to stay within the described area to grow larger diamonds.Therefore, the method portion of this invention is to raise thetemperature and pressure to a particular diamond forming area within aparticular region defined by a given catalyst; where the area is closelyadjacent a curve of the diamond forming region defined by an equilibriumline between graphite and dia mond, and to maintain the temperatureconstant with respect to time in that area to provide the desiredcrystal formaion.

There are several methods generally available for reaching this area.One of these methods is somewhat less than satisfactory with theparticular apparatus described. From examination of FIG. 6 and bearingin mind the operation of the press apparatus, it may be seen that at oneatmospheric pressure the temperature of the apparatus may be raised toapproach the vicinity of the temperature in the shaded area andthereafter the pressure raised so that the combined pressure temperaturepoint lies within the lower portion of the shaded area. This operationis rather unsatisfactory since raising of temperature previous toraising of pressure affects the operation of the apparatus. Pressurerise will not follow along a vertical line but will fluctuate widely.Temperature will also fluctuate. With further improvements and/or otherapparatus such a procedure as just described may be employed to reachthe area desired or various incremental steps of increasing temperatureand/ or pressure may be employed to reach the area. For the pur poses ofthis invention, with the apparatus as described for FIG. 2, thefollowing procedures are more satisfactory depending on the size ofreaction vessel employed, in temperature response time, and total timeof operation. For example, when using a small reaction vessel of thesize described with relation to the prior art apparatus description ofFIG. 2, the time temperature constant of such a reaction vessel is verysmall, that is, with the application of electrical power the temperaturerises extremely rapidly to a high point and tapers off gradually;therefore, with a small reaction vessel, pressure is applied to raisethe pressure to, for example, a point P1, FIG. 6. Thereafter, electricalpower is applied to raise the temperature to a point T1. Raising of thepressure and temperature in this order results in a temperature risewhich does not affect the pressure point P1 to any appreciable degree.However, the temperature should be held at point T1, a thresholdtemperature, for the following reasons. If an attempt were made to reachtemperature T2 immediately even though the temperature time rise isextremely small, chances are excellent for overshooting the mark andending about T3 which is in the non-diamond or graphite stable region,and variances of temperature back and forth between the diamond growingregion and the non-diamond or graphite stable region affects thereaction to a considerable degree. Secondly, since the time temperaturerise levels out gradually after a very rapid rise, the period of timenecessary to change the temperature from T1 to T2 may be so extensivethat diamonds are formed in the reaction vessel in that pediod of timeand in that range between temperature T1 and the shaded area so thatdiamonds start to form in the region of poor growth affecting thequality of the diamond then grown in the shaded area. Therefore, themethod of raising the temperature to point T1 permits the reactionvessel temperature and pressure to become stabilized in the non-diamondgrowing region before diamond growth and thereafter only a smalltemperature rise is necessary to proceed immediately to T2 in the shadedarea. After temperature T1 is reached and stabilized, more power isadded to the reaction vessel to raise the temperature in a matter of afew seconds to T2 in the shaded area and because of the rapidity oftemperature rise from T1-T2 very few, if any, diamond crystals are grownprior to reaching the shaded area. The temperature may thereafter becontrolled in the shaded area for varying periods from a few minutes toseveral hours to grow larger diamond crystals.

In proceeding to larger size reaction vessels and generally to thosevessels presently employed, the time temperature rise is again muchslower (up to 15 minutes, for example) because of the larger volume. Itis, therefore, difficult to stop at a temperature T1 and then proceedwith the foregoing described satisfactory method. The method employedwith larger reaction vessels is as follows. Pressure is raised to apoint P2 corresponding to T2. Thereafter, electrical power is increasedto raise the temperature as rapidly as possible so that the temperaturecurve proceeds immediately through T1 and also through T2 to stop at apoint, for example, T3. It so happens in this method that in proceedingfrom T1 to T2, diamonds may be grown from graphite, but regardless ofthe size or quality the increase in temperature to the point T3 resultsin regraphitization of the diamonds so that conditions exist at point T3where no diamonds are formed nor are in existence in the reactionvessel. Thereafter, the temperature is descreased, a decrease which ispossible by the improvements in the reaction vessel described to thepoint T2 and thereafter maintained as close to the line DB as possible.Here, only the larger size diamond crystals are formed.

The results of the practice of the teachings of this invention aremarkedly distinctive. Where prior practices result in a diamond sizeranging Well under /2 mm., this invention produces diamond crystalsgreater by a factor of 4. Specific examples of the teachings of thisinvention are as follows:

Example I A reaction vessel (34 of FIG. 2 approximately inch diameterand inch in length) was assembled with a substantially pure nickel slugin the hollow core and a spectroscopically pure graphite slug at eachend of the nickel slugs to fill the core. Pressure on the reactionvessel was raised to about 78,000 atmospheres. Temperature wasstabilized to about 1350" C. and thereafter increased to about 1450 C.in from l-3 seconds. This temperature was maintained for about 10minutes. Upon removal from the press, the reaction vessel was found tocontain several diamond crystals from .2 to .4 mm. in the longerdimension.

Example 2 The procedure of Example 1 was followed but with a nickelchromium catalyst of nickel and 20% chromium (by weight) and thereaction vessel of FIG. 4 (about inch diameter and 1 inch in length).Threshold temperature was 1250 C., maximum pressure was 72,000atmospheres, maximum temperature was 1320 C. Elapsed time was about 2hours. Upon removal of the reaction vessel from the press, it was foundto contain 3 diamond crystals from /2 to 2 mm. average diameter.

Example 3 The procedure and reaction vessel of Example 2 was againfollowed but with a nickel iron catalyst, 35% nickel, 65% iron (byweight). Maximum pressure was 66,000 atmospheres, threshold temperaturewas about 1150 C., maximum temperature about 1250" C., and elapsed time3 hours. Upon removal of the reaction vessel from the press, it wasfound to contain several diamond crystals somewhat smaller than 2 mm.average.

Example 4 The procedure, reaction vessel, and catalyst of Example 3 wasfollowed wherein temperature was quickly increased to pass through thediamond growing region to stabilize, out of said region, about 1400 C.The temperature was thereafter reduced to about 1250 C. and maintainedfor about 1 /2 hours. Upon removal of the reaction vessel, it was foundto contain several diamond crystals of about 1.5 mm. in the longerdimension.

Since diamond forming regions of pressures and temperatures have beenpreviously ascertained and diamonds obtained incontrovertibly proven asdiamonds, exhaustive tests of the diamond produced by this inventionwere not necessary. X-ray diffraction patterns were, however, made forother purposes and did show true diamond pattern. These diamondsscratched sapphire, withstood acid cleaning tests, and burned in oxygenleaving inconsequential amounts of residue. It is understood, from thisdescription, that this invention discloses means and methods for thegrowing of larger diamond crystals of no limitation with respect tomethod and contemplates a combination of a predetermined area ofpressures and temperatures together with constant temperatures andpreferred reaction vessel configurations to be employed with constanttemperatures. It is understood that the method and apparatus may beemployed for any carbonaceous material, the graphite being merelyexemplary for this application. Broadly speaking, any carbon-containingmaterial may be employed which when heated will carbonize and formgraphite before the diamond reaction takes place. Diamonds have beenproduced when the initial material has been carbon, wood, pitch,adamantane, etc.

The invention is also applicable to the growth of various crystals wherean equilibrium line of pressure and temperature exists, wheretemperature control is desirable and where it is not desirableto passcurrent through the reactant material. For example, this invention isapplicable to crystal growth of silicon, germanium, etc., as Well as tothe cubic form of boron nitride disclosed and claimed in copendingapplication S.N. 707,434, Wentorf, filed January 6, 1958, now US. Patent2,947,617, and assigned to the same assignee as the present invention.

While other modifications of this invention and variations of apparatusand methods which may be employed within the scope of the invention havenot been described, the invention intended to include all such as may beembraced Within the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a method of producing diamond crystals from a combination of anon-diamond carbon together with a catalyst which includes subjectingthe said non-diamond form of carbon and the catalyst to high pressuresand high temperatures above the graphite-to-diamond equilibrium line onthe phase diagram of carbon to provide diamond growth from saidnon-diamond carbon, the improvement of growing larger diamondscomprising, raising the said pressure and temperature to that range ofpressures and temperatures in the diamond growing region for the givencatalyst, above the said graphite-todiamond equilibrium line on thephase diagram of carbon, at a point closely adjacent the said graphiteto diamond equilibrium line and above the cube region wherein diamondscrystallize predominantly in cube form, maintaining the temperatureconstant over an extended period of time at said point, reducing thetemperature and pressure, and recovering diamond so grown.

2. In a method of producing diamond crystals from the combination ofnon-diamond carbon together with a catalyst which includes subjectingthe said, combination to combined pressures and temperatures above thegraph.- ite to diamond equilibrium line on the phase diagram of carbonto provide diamond growth from said non-diamond carbon, the improvementof producing larger crystals comprising, raising the pressure to abovethe said graphite to diamond equilibrium line and within the diamondforming region of the given catalyst at a temperature less than existingin said region, increasing the temperature to a point corresponding tosaid pressure and adjacent to but outside of the diamond forming regionof the said given catalyst, maintaining this threshold temperature forstabilization purposes, thereafter increasing the temperature on saidcombination of catalyst and non-diamond carbon to a point closelyadjacent and above the graphite to diamond line and above the cuberegion wherein diamond crystallizes predominantly in cube form,maintaining temperature constant over an extended period of time at saidpoint, reducingsaid temperature and pressure, and recovering diamond sogrown.

3. In a method of producing diamond crystals from a combination of anon-diamond. carbon together with a catalyst which includes subjectingsaid combination to pressures and temperatures above the graphite todiamond equilibrium line on the phase diagram of carbon to providediamond growth from said non-diamond carbon, the improvement ofproducing large crystals comprising, raising the pressure to aboutopposite a point in the diamond forming region of the given catalyst andoutside of said diamond forming region, increasing the temperature onsaid combination for the temperature curve to pass from outside the saiddiamond forming region through the said diamond forming region for thegiven catalyst and thereafter into the non-diamond form of graphiteregion, maintaining the pressure and temperature conditions forstabilization in the non-diamond form of graphite region, thereafterreducingthe temperature until a point is reached in the diamond formingregion for the given catalyst at a point closely adjacent and above thegraphite to diamond line and slightly above the cube region, maintainingthe temperature constant at this point over an extended period of time,reducing said temperature and pressure, and recovering diamond so grown.

4. The invention as claimed in claim 3 wherein said temperature pointabove and closely adjacent the graphite to diamond line is within about50 C. thereof.

5. A method of producing large diamond crystals from the combination ofa non-diamond carbon together with a catalyst taken from the metalsconsisting of those metals of group Vill of the periodic table ofelements, chromium, manganese and tantalum, and alloys of these metalswhich comprises subjecting said non-diamond carbon and catalyst to apressure generally corresponding to a temperature in the diamond formingregion of said catalyst, employing an indirectly heated reaction vesselto ,eat said catalyst and non-diamond carbon to a temperature generallycorresponding to said pressure and lying within the diamond formingregion of the given catalyst above the cube region where diamondcrystallizes predominantly in cube form and closely adjacent thegraphite to diamond dividing line, maintaining the temperature constantfor an extended period of time at said point, reducing said temperatureand pressure, and recovering diamond so grown.

6. The invention of claim 5 wherein said indirectly heated reactionvessel comprises in combination, a thermally insulating and electricallynonconductive vessel having an opening therein, a relatively thinelectrically conductive heater tube positioned Within said opening andcontiguous with said vessel, a hollow electrically conductive andthermally insulating cylinder positioned concentrically within andcontiguous with said heater tube, a diamond catalyst metal cylinderwhose length is less than that of said tube positioned concentricallywithin said tube and contiguous therewith, a non-diamond form of carbonwithin said catalyst cylinder, an electrically nonconductive and thermalinsulating stone plug positioned within said heater tube adjacent oneend of said heater tube and non-diamond form of carbon to provide asubstantially solid reaction vessel, an electrically conductive disc oneach end of said heater tube and vessel and in contact therewith, sothat an electrical current applied to said end discs flows through saidheater tube to indirectly heat the combination of the catalyst and anon-diamond form of carbon.

7. The invention as claimed in claim 5 wherein said indirectly heatedreaction vessel comprises in combination, a first hollow stoneelectrically nonconductive and thermally insulating cylinder, anelectrically conductive graphite heater tube positioned concentricallywithin and contiguous with said hollow cylinder, a hollow electricallynonconducting and thermally insulating second stone cylinder positionedconcentrically within said heater tube and contiguous therewith, acatalyst metal tube of less axial dimension than said first cylinderpositioned within and concentrically with said second cylinder andcontiguous therewith, a non-diamond form of carbon within said catalysttube, a stone plug positioned Within said reaction vessel on each endthereof to provide a solid cylindrical configuration, an electricallyconductive metal disc positioned on each end of said reaction vessel sothat current applied to said end discs flows through said graphiteheater tube to indirectly heat the combination of carbon and catalystmetal in said reaction vessel.

8. The invention as claimed in claim 5 wherein said indirectly heatedreaction vessel comprises in combination, a hollow electricallynonconducting and thermally insulating stone vessel, a thin graphiteheater tube positioned within and contiguous with said vessel, a hollowcylindrical electrically nonconductive and thermally insulating stonecylinder positioned with said heater tube and contiguous therewith, ametal catalyst cylinder positioned within said second stone cylinder andcontiguous therewith, said catalyst cylinder being axially shorter thanthe said first cylinder, an annulus of a non-diamond form of carbonpositioned Within said catalyst metal tube and contiguous therewith, asecond cylinder of catalyst metal positioned within said non-diamondcarbon annulus and contiguous therewith, a central core of stonematerial positioned within said latter catalyst cylinder, a plug ofstone material positioned within said heater tube in one end of saidreaction vessel to provide a substantially solid vessel, a pair ofelectrically conductive metal discs positioned on each end of saidvessel and in contact with said heater tube so that current applied tosaid end discs flows through said heater tube to indirectly heat saidcarbon and catalyst.

9. An indirectly heated reaction vessel comprising in combination, ahollow electrically nonconductive and thermally insulating vessel, athin electrically conductive heater tube positioned within andcontiguous with said vessel, a hollow electrically nonconductive andthermally insulating cylinder positioned concentrically within andcontiguous with said heater tube, a metallic cylinder whose length isless than that of said tube positioned concentrically within said tubeand contiguous therewith and adapted to contain a reactant material, anelectrically nonconductive and thermal insulating plug positioned withinone end of said reaction vessel to provide a substantially solidreaction vessel, an electrically conductive disc on each end of saidheater tube and in contact therewith so that an electrical currentapplied to said end discs flows through said heater tube to indirectlyheat the combination of the catalyst and reactant.

10. An indirectly heated reaction vessel comprising in combination, ahollow electrically nonconductive and thermally insulating cylinder, athin electrically conductive heater tube positioned concentricallywithin and contiguous with said cylinder, a hollow electricallynonconductive and thermally insulating cylinder positionedconcentrically within and contiguous with said heater tube, a' diamondcatalyst metal cylinder whose length is less than that of said tubepositioned concentrically within said tube and contiguous therewith, anon-diamond form of carbon within said catalyst cylinder, anelectrically nonconductive and thermal insulating plug positioned withinone end of said reaction vessel to provide a substantially solidcylindrical vessel, an electrically conductive disc on each end of saidcylinder and in contact therewith so that an electrical current appliedto said end discs flows through said heater tube to indirectly heat thecombination of the catalyst and a non-diamond form of carbon.

11. An indirectly heated reaction vessel comprising in combination, afirst hollow electrically nonconductive and thermally insulating stonecylinder, a graphite heater tube positioned concentrically within andcontiguous with said hollow cylinder, a second hollow electricallynonconducting and thermally insulating stone cylinder positionedconcentrically within said heater tube and contiguous therewith, acatalyst metal tube of less axial dimension than first cylinderpositioned within and concentrically with said second cylinder andcontiguous therewith, a non-diamond form of carbon within said catalysttube, a stone plug positioned within said reaction vessel on one endthereof to provide a solid cylindrical configuration, an electricallyconductive metal disc positioned on each end of said reaction vesselsuch that current applied to said end discs flows through said graphiteheater tube to indirectly heat the combination of carbon and catalystmetal in said reaction vessel.

12. An indirectly heated reaction vessel comprising in combination, afirst hollow electrically and thermally nonconducting stone cylinder, athin graphite heater tube positioned concentrically within andcontiguous with said cylinder, a second hollow cylindrical electricallynonconductive and thermally insulating stone cylinder positioned withinsaid heater and contiguous therewith, a metal catalyst cylinderpositioned within said second stone cylinder and contiguous therewith,said catalyst cylinder being axially shorter than the said firstcylinder, an annulus of a non-diamond form of carbon positioned withinsaid catalyst metal tube and contiguous therewith, a second cylinder ofcatalyst metal positioned within said nondiarnond carbon annulus andcontiguous therewith, a central core of stone material positioned withinsaid latter catalyst cylinder, a plug of stone material positionedwithin said heater tube at one end of said reaction vessel to provide asubstantially solid cylinder, a pair of electrically conductive metaldiscs positioned on each end of said cylinder and in contact with saidheater tube so that current applied to said end discs flows through saidheater tube to indirectly heat said carbon and catalyst.

13. A method of growing large diamond crystals comprising incombination, subjecting graphite and an alloy metal catalyst taken fromthe group consisting of those metals of group VIII of the periodic tableof elements, manganese, tantalum and chromium, to a temperature andpressure lying above the graphite to diamond dividing line on the phasediagram of carbon in the diamond forming region for the particularcatalyst employed and above the cube region where diamond crystallizespredominantly in cube form, and closely adjacent the said dividing line,maintaining the temperature constant and within 50 C. of said line for aperiod of time in the range of at least about 2 minutes to several hoursand thereafter reducing the temperature and pressure and recoveringdiamond formed.

14. A method of growing large diamond crystals comprising incombination, subjecting graphite and a metal catalyst which includesnickel to a temperature and pressure lying above the graphite-to-diamonddividing line on the phase diagram of carbon and out of the diamondforming region for said catalyst, reducing the temperature to a pointlying within the diamond forming region for said catalyst above thegraphite to diamond equilibrium line and within about 50 C. of saidline, maintaining the temperature constant for a period of time fromabout 2 minutes to several hours and thereafter reducing the temperatureand pressure and recovering diamond grown.

15. In a method of producing diamond crystals from the combination of anon-diamond carbon together with a catalyst which includes subjectingthe said combination to combined pressures and temperatures above thegraphite to diamond equilibrium line on the phase diagram of carbon toprovide diamond growth from said non-diamond carbon, the improvement ofproducing larger diamond crystals comprising, raising thepressure-temperature conditions to a point where said conditions areoutside. of those conditions existing within the diamond forming regionof the given catalyst and at a point closely adjacent to and below saidgraphite to diamond equilibrium line, maintaining the said conditions atsaid point for stabilization purposes for a period of time, thereafterchanging these conditions from said point to a further point closelyadjacent to and above the graphite-to-diamond line and above the cuberegion where diamond crystallizes predominantly in the cube form,maintaining said pressure-temperature conditions at this point constantover an extended period of time, reducing said pressuretemperatureconditions, and recovering diamonds so grown.

1. IN A METHOD OF PRODUCING DIAMOND CRYSTALS FROM A COMBINATION OF ANON-DIAMOND CARABON TOGETHER WITH A CATALYST WHICH INCLUDES SUBJECTINGTHE SAID NON-DIAMOND FORM OF CARBON AND THE CATALYST TO HIGH PRESSURESAND HIGH TEMPERATURES ABOVE THE GRAPHITE-TO-DIAMOND EQUILIBRIUM LINE ONTHE PHASES DIAGRAM OF CARBON TO PROVIDE DIAMOND GROWTH FROM SAIDNON-DIAMOND CARBON, THE IMPROVEMENT OF GROWING LARGER DIAMONDSCOMPRISING, RAISING THE SAID PRESSURE AND TEMPERATURE TO THAT RANGE OFPRESSURES AND TEMPERATURES IN THE DIAMOND GROWING RAEGION FOR THE GIVENCATALYST, ABOVE THE SAID GRAPHITE-TODIAMOND EQUILIBRIUM LINE ON THEPHASE DIAGRAM OF CARBON, AT A POINT CLOSELY ADJACENT THE SAID GRAPHITETO DIAMOND EQUILIBRIM LINE AND ABOVE THE CUBE REGION WHEREIN DIAMONDSCRYSTALLIZE PREDOMINANTLY IN CUBE FORM, MAINTAINING THE TEMPERATURECONSTANT OVER AN EXTENDED PERIOD OF TIME AT SAID POINT, REDUCING THETEMPERATURE AND PRESSURE, AND RECOVERING DIAMOND SO GROWN.
 9. ANINDIRECTLY HEATED REACTION VESSEL COMPRISING IN COMBINAATION, A HOLLOWELECTRICALLY NONCONDUCTIVE AND THERMALLY INSULATING VESSEL, A THINELECTRICALLY CONDUCTIVE HEATER TUBE POSITIONED WITHIN AND CONTIGUOUSWITH SAID VESSEL, A HOLLOW ELECTRICALLY NONCONDUCTIVE AND THERMALLYINSULATING CYLINDER POSITIONED CONCENTRICALLY WITHIN AND CONTIGUOUS WITHSAID HEATER TUBE, A METALLIC CYLINDER WHOSE LENGTH IS LESS THAN THAT OFSAID TUBE POSITIONED CONCENTRICALLY WITHIN SAID TUBE AND CONTIGUOPUDTHEREWITH AND ADAPTED TO CONTAIN A REACTANT MATERIAL, AN ELECTRICALLYNONCONDUCTIVE AND THERMAL INSULATING PLUG POSITIONED WITHIN ONE END OFSAID REACTION VESSEL TO POVIDE A SUBSTANTIALLY SOLID REACTION VESSEL, ANELECTRICALLY CONDUCTIVE DISC ON EACH END OF SAID HEATER TUBE AND INCONTACT THEREWITH SO THAT AN ELECTRICAL CURRENT APPLIED TO SAID ENDDISCS FLOWS THROUGH SAID HEATER TUBE TO INDIRECTLY HEAT THE COMBINATIONOF THE CATALYST AND REACTANT.